Field of the Invention
The present invention relates to a contact pin utilized for a socket for electrical parts for detachably accommodating and holding an electrical part such as a semiconductor device (called as xe2x80x9cIC packagexe2x80x9d hereinlater), and also related to a socket for electrical parts provided with such contact pin.
Related Art of the Invention
In a known art, there has been provided an IC socket, as xe2x80x9csocket for electrical partsxe2x80x9d mentioned above, for carrying out performance test of an IC package as xe2x80x9celectrical partxe2x80x9d, which is preliminarily disposed on a printed circuit board and in which an IC package is accommodated in this IC socket to thereby establish an electrical connection between the IC package and the printed circuit board.
As such IC package, there is provided one having, for example, a rectangular body having a side portion from which a number of terminals extends sideways.
Under the state that the IC package is accommodated in the IC socket, when contact portions of contact pins of the IC socket contact a number of terminals of the IC package, respectively, the terminals and the printed circuit board are electrically connected through the contact pins.
Such contact pin is formed by being punched out from a metal thin plate having conductivity, by means of press working, for example, and under the punched-out condition, the punched-out, i.e., cut, portion has a rough surface condition.
When the IC package is accommodated in the IC socket, a contact portion of a contact pin contacts a terminal of the IC package and slightly slides (wipes). According to this motion, a plating surface (layer) of the terminal is slightly cut to thereby remove an oxidation film or the like on that surface and, hence, make good the conductivity between the contact portion of the contact pin and the terminal of the IC package.
However, in the known structure mentioned above, at a time when the rough or course cut surface is provided to the contact portion of the contact pin at the time of punching out the contact pin from the metal thin plate, a solder will be easily transferred to the surface of the contact portion in a case where the terminal of the IC package is plated with a solder. This will result in the difficulty for maintaining, in good condition, the stable contact state between the contact portion of the contact pin and the terminal of the IC package for a long term. Furthermore, in a case where the plating of the terminal of the IC package is, for example, palladium plating, applicable to a lead-free requirement, the plating (plated) layer will provide a thin thickness in comparison with the solder plating, so that there is a fear that the plating layer is broken and the base surface of the terminal is exposed, providing inconvenience and being defective.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a contact pin used for a socket for electrical parts capable of maintaining, in good condition, a stable contact state between a contact portion of a contact pin and a terminal of an electrical part for a long term and preventing breakage of a plating layer of the terminal, and also provide a socket for electrical parts having the contact pin having the improved structure mentioned above.
This and other objects can be achieved according to the present invention by providing, in one aspect, a contact pin for an electrical part formed from a metal material having conductivity and having a contact portion contacting a terminal of the electrical part, wherein the contact portion is polished by polishing means.
According to this aspect, the contact portion of the contact pin is polished by the suitable polishing means, and accordingly, in a case where the contact portion of the contact pin slides on the terminal of the electrical part, the plating layer formed on the terminal can be prevented from being broken and the lead base material thereof can be also prevented from being exposed outside. Moreover, a transferring amount of the solder can be controlled, so that the contact stability can be effectively maintained.
In a preferred embodiment of this aspect, the polishing of the contact portion is performed without applying any external force thereto. The polishing is a chemical polishing. A nickel plating is effected to the contact portion to which the chemical polishing has been made.
The terminal of the electrical part on which the contact portion of the contact pin slides is effected with a plating layer having a thickness of not more than 1 xcexcm.
The polished contact portion has a surface roughness which is smaller than a thickness of a plating layer formed on the terminal.
According to the preferred embodiment mentioned above, the contact pin even being small in size and weak in strength can be polished without deforming the same, by such as chemical polishing, by applying no external mechanical force. According to the chemical polishing treatment, a number of contact pins can be polished at the same time by, for example, dipping them in a polishing solution, thus improving the workability for manufacturing the contact pins. The nickel plating will compensate the reduction in thickness of the contact pin including the elastic portion through the polishing treatment and, hence, the elastic strength of the elastic portion will be maintained.
Furthermore, when the contact portion, which has been polished, slides on the terminal to which the plating is effected to provide a thickness of not more than 1 xcexcm, the peeling-off of the plating surface can be effectively prevented by the polished surface of the contact pin. Still furthermore, by setting the surface roughness of the contact portion polished by the polishing means to be less than a thickness of the plating layer of the terminal, the peeling-off of the plating layer will be effectively prevented.
In a modification of the above aspect of the present invention, there is also provided a contact pin for a socket for an electrical part formed from a metal material having conductivity, comprising:
a base portion;
a stationary piece extending from the base portion and contacting the electrical part; and
a movable piece extending from the base portion and contacting the electrical part,
the movable piece comprising an elastic portion and a contact portion contacting the electrical part, the contact portion being polished.
In another aspect of the present invention, there is also provided a socket for an electrical part having a terminal comprising:
a socket body to which an electrical part is mounted;
an operation member provided for the socket body to be vertically movable in an operative state, the operation member being formed with a cam portion;
a contact pin provided for the socket body, the contact pin being formed from a metal material having conductivity and comprising an elastic portion elastically deformable, a contact portion formed on a tip end portion of the elastic portion and adapted to contact the terminal of an electrical part, and an operation piece to be pressed by the cam portion of the operation member,
the contact portion being polished by polishing means,
the elastic portion being elastically deformed when the operation member is moved downward and the operation piece of the contact pin is pressed by the cam portion of the operation member to thereby separate the contact portion from the terminal of the electrical part.
In this aspect, the socket may be an IC socket provided with a number of contact pins and the electrical part may be an IC package provided with a number of IC leads as the terminals.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.